Tubing



United States Patent Inventors Rocco Falcomato [56] R f e e Cit dBrooklyn; UNITED STATES PATENT Jacob A.Almouli, Forest Hills, New York 3037 529 6/1962 H S A I No 730 235 ancl l38/l44 3,080,893 3/1963Craycraft 138/144 May 1968 3 267 968 8/l966 Foll m1 138/141 PatentedDec. 8, 1970 1 Assignee Niemand Bros. Inc. Primary Examiner-Laverne D.Geiger Elmhurst, New York Assistant ExaminerRichard J Sher a corporationof New York Attorney Kane, Dalsimer, Kane, Sullivan and Kurucz TUBING 7Claims, 4 Drawing Figs.

US. Cl. 138/144,

l6l/2l4, 161/227 ABSTRACT: A dimensionally stable tube, particularly foruse Int. Cl. Fl6l 9/16 with a voice coil, formed of three layers, afirst layer having Field ofSearch 138/144, structural integrity anddimensional stability, 3 second layer ymi g acting synergistically withthe first to retain the structural inl6l/227, 214 tegrity.

Cl/T L UI l In various applications tubular members of exceptionaldimensional stability are necessary. As a particular example, a voicecoil tubewhich actuates the speaker diaphragm of a speaker assemblycannot properly perform its function without being formed as an almostperfect hollow cylinder, and maintaining this configuration throughoutits life. In most speaker assemblies, such as in radio, television, andhigh fidelity phonograph speakers, this voice coil tube isconnected tothe diaphragm, and a coil of wire is wrapped around the voice coil tube,the coil carrying impulses from the electronic circuitry of the system.These electrical impulses are transformed into'the sound emanating fromthe speaker through the action of the voice coil tube on the diaphragm.If the tube assumes a shape which'is slightly out of round, the resultis a distortion in the sound produced by the speaker.

Two methods have previously been employed in the prior art to form thesevoice coil tubes, both methods suffering certain deficiencies as willbernorefully set forth below. In the first method, a blank was cut froma relatively thin sheet of aluminum; This aluminumblank was bent intothe hollow cylindrical configuration to form the voice coil tube.However, the formation of a perfect circle was extremely difficult and,as it was almost impossible to reform the blank, there was a great dealof waste material.

The second method employed in the prior an involved the spiral windingof a plastic-impregnated paper. The resulting tube lacked bothdimensional and water stability. The plastic impregnation, if keptwithirrthe proper limits such that the ultimately formed tube couldfunction in the desired application, did not impart sufficient waterresistance to the paper, or stiffness to the structure,,to provide thetube with the necessary properties. I In accordance with the. presentinvention, we have developed a structure for av oice coiltube which canbe formed economically andwhich has dimensional stability and structuralintegrity, even when subjected to heat and highatmospheric humidity.

SUMMARY THE INVENTION In accordance with.the,-present invention, we havefound that a dimensionally stable tube, particularly for use wit voicecoils, can be formed as a two layer structure.

The first layer of the tube'is a dimensionally stable material which isrelatively stiff and resilient. l

Several properties are required ofthe second layer. First,it must havethe type of surface which aids in bonding of the wire coil to be wrappedaround the ultimately formed tube. Secondly, it must be heat stable andrelatively moisture resistant. Because of these latter two properties,it aids, synergistically, in making the overall tube dimensionallystable.

The tube can have a third layer, particularly when it is used as a voicecoil tube, of a thermosetting resinous layer. While each of the layersmust be thin, particularly when the structure isv to be employed as avoice coil tube, this last, thermosetting layer is extremely thin. The,primary function of this outer layer is to provide a surface which iscompatible with the insulation of the wire which is coiled about thetube. It must also cover the second layer as an aid in providingstability of the overall structure in the presence of atmospherichumidity.

The overall structural integrity and dimensional stability of the tubeare greatly enhanced when the first two layers are formed by spiralwinding.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

I FIG. I shows a section of a tube having the structure of the 2 FIG. 4is a speaker assembly including a portion of the tube of FIG. 1, cut tosize for use in the application.

DESCRIPTION or THE PREFERRED EMBODIMENTS As previously indicated,'thetube of the present invention is preferably formed by a spiral windingoperation. Such an operation, and i the equipment necessary, aregenerally described in the copending application of Rocco Falcomato andZdenek Krajca, Ser. No. 554,287, filed May '26 1966, now abandoned forPlastic Tubes and Method of Making the Same," and assigned to the sameassignee as the present invention. That portion of the referencedcopending application is hereby incorporated, by reference. r

In general, the spiral winding operation involves the use of a smoothmandrel having a diameter equal to the'desired inner diameter of thetube to be formed. The first layer of spirally wound material is wrappedaround the mandrel and is driven by an endless belt. Preferably, theside of the strip which comes in contact with the mandrel is coated withan inert lubricant in order to assist movement of the strip on themandrel. The second spirally wound layer is then placed over the firstand the composite structure is drivenby an endless belt. Theundersurface of the second spirally wound layer can be coated with anadhesive prior to application to the first formed tube, in order topromote adhesion between the two layers. Similarly, eachof thesurfaceswhich is to be joined can be coated with an adhesive prior to winding ofthe second layer.

In accordance with the present invention, a tube 1 is formed inaccordance with aspiralwinding operation similar to that describedabove. A first layer 2 of the dimensionally stable, stiff and resilientmaterial is first wrapped onto the mandrel. This layer 2 thus forms theinner layer of the formed tube. The width of the tape used to form thislayer is generally between 1% inches and 3 inches, but is preferablybetween about 1% and] /2 inches. The diameter of the mandrel on whichthe first layer is placed, and thus the inner diameter of the formedtube is generally from about it to 3 inches. Preferably, for use invoice coil tubes, this inner diameter is from about a inch to 1% inches.I

The angle of approach of the tape of this first layer, with respect tothe mandrel, is generally from about 25 to but most preferably is atabout 45. This angle of approach, obviously determines theangle 3 of thevarious courses of the material within the tube. The tension placed onthe tape as it is wound onto the mandrel is generally between about 4and10 pounds, and the degree of tension varies directly with the ply andwidth of the layer being wrapped. The layer is formed on the mandrel bybutt joining the successive courses of tape, without adhesive.

The tape employed can be varied in thickness from about I to 2 mils.This will be related to the overall dimensions of the tape to bedescribed later. The materials employed in forming this layer of thetube, as previously described, must be relatively stiff and resilient.Materials which are particularly suited generated in operation of avoice coil tube, to make them useful in this structure.

The second layer 4 of material for the tube is also spirally wound ontothe mandrel, over the first layer 2. The tape dimensions and conditionsof wrapping are the same as those set forth above with respect to thefirst layer of the tube. However, the thickness of the film used for thesecond layer generally varies from about 2 mils to 3 mils. The secondlayer 4 of tape is so wound onto the mandrel that the butt joints do notoverlap and, preferably, the butt jioints of the second layer fall inthe center of the courses of the first layer. As with the first layer,the butt joints are formed without adhesive.

Prior to winding the second layer 4 onto the first layer 2, an

.1 adhesive Sis appliedto'the undersurfaceof the tape forming the secondlayer 4. The presence of thisadhesive layer 5 is clearlyindicated intheenlarged view of FIG. 2. The type of adhesive employed varies withthe use to which the tube will be put. Forexample, when the tube issubjected to a heat which is not considered excessive, i.e., not morethan about a polyimide adhesiveis:

12 percent Polyimide resin: and

88 percent Mixture of methyl pyrrolidine and acetamide.

For example, DuPont Pyre ML RK-692 can be employed in this application.

The purpose of the second layer 4 is to provide resistance to heatandhumidity and also to provide a surface for bonding of electricalelements to the tube. Preferred materials for use in this layer aretheKapton film, described with respect to the 1 first layer 2, and. a tapeformed of Nomex. Nomex is a polyamide paper, and thus constitutes afibrous material extremely resistant to high temperatures. Q j ingeneral, if the first layer 2 is formed of an aluminum film,

then the second layer 4 is formed of a Kapton film or Nomex patible withthe electricalelements to be bonded.

In general, these electrical elements comprise an electrical wire whichis coated with an insulating layer of a synthetic resin. Thus, thepreferred material for the layer 6 is a crosslinked synthetic resinsystem, of the same type as that employed for the wire insulation. Forexample, the material can be a phenolic resin.

As previously noted, the only requirement for the thermosetting resinouslayer 6 is that it cover the second layer 4. Thus, it is applied in asthin a layer as possible to accomplish this purpose. In general, thethickness of this thermosetting layer 6 should be about mil.

For use in voice coil tube applications, the overall thickness of thetube should generally be from about 3 to 6 mils, depending upon the usetowhich the tube is to be put. Depending upon the specification of tubethickness, this thickness must be maintained within a tolerance of abouti 1% mil, and the internal diameter of the tube must be maintained to atolerance of about :L l milsSuch fine tolerances can best be maintainedby formationof a structure as described in this invention.

Employingthe structureof this invention, the formed tube inherentlypossesses the desired properties of structural integrity and.dimensionalv stability. If the wall thickness is reduced below thedesiredlevel, then there is insufficient structural integrity, while ifthe wall is thicker than that specified, then excessive heat isgenerated in operation, because of, the excessive power requirements togenerate sound.

paper, while if the first layer is formed of a Kapton film, then thesecond layer is formed of Nomex paper. However, in certain specialapplications, both layers can be formed of Kapton The following exampleillustrates preparation of a tube having the structure of the presentinvention. The tube was formed with an internal diameter of 1.5 inches,a wall thickness of 3'mils, and a length of 18 inches. Thus, the mandrel employed for formation of the spirally wound tube had a diameter of1.5 inches. One layer of 1 mil thick aluminum foil film having ahardness of 11-18 was wrapped around this mandrel asa first layer. Atension of about 6 pounds was maintained on the tape during winding andthe angle of approach was 65. The layer was coated with a polyesterbased adhesive,

having the formula previously set forth, and this adhesive was broughtto atacky state by partially vaporizing the solvents from it.

The second layer, overwrapped on the. first, was a 2 mil thick, Nomexpaper tape having a width of l inches. The underside of this layer wasalso coated with a polyester based adhesive which was partially dried,again, to bring the adhesive to the tacky state. The tension on thistape, during application, was also about 6 pounds and its angle ofapproach was the same as that of the aluminum foil film. The twoadhesive sides were applied in juxtaposition to bond the first aluminumfoil film to the second Nomex paper film, with the butt joints of theNomex lying between those of the aluminum foil.

The wound tube was thenpassed through a metering coating applicatorwhere a phenolic based resin was deposited on the surface in an amountsufficient to cover the N omex layer.

This phenolic resin was then dried. As the tube was removed.

from the mandrel, a flying cutoff saw cut the tube in two inch lengths,suitable for use as a voice coil tube.

The application of the shorter lengths of the tube for usein Wrappedaround the tube, in several layers, is an insulated wire 9 whichtransmits electrical impulses from the electronic system of a radio,television set, high fidelity phonograph, or other similar system.

Thus, an improved structure for a tube having structural integrity anddimensional stability has been shown. These tubes are superior to thoseof the prior art and can be formed in a more facile manner.

We claim:

1. A tube having structural integrity and dimensional stability andformed of:

a. a first layer of a film of a material selected from the classconsisting of hard aluminumand polyimide;

b. a second layer formed from a film of a material selected from theclass consisting of poly'amide and polyimide; and

c. a thermosetting phenolic resinous layer.

2. The tube of claim 1 wherein the first and second layers are spirallywound.

3. The tube of claim 1 wherein the successive courses of the spirallywound material are butt joined in the absence of adhesive, and the buttjoints of the second layer lie within the coursesof the first layer.

4. A tube having structural integrity and dimensional stability for usein a voice coil attached to the diaphragm of a sound speaker comprising:

a. a first spirally wound layer formed from a film of a materialselected from the class consisting of hard aluminum and polyimide,wherein said film has a thickness of from 1 to 2 mils;

b. a second spirally. wound layer formed of a film of a materialselected from the class consisting of polyamide and-polyimide, whereinsaid film has a thickness of from 2 to 3 mils; and c. a layer. of athermosetting phenolic resin, the thickness of the resinous coatingbeing only sufficient to cover the second layer; and the overallthickness of the tube being between about 3 and 6 mils,

5. The tube of claim 4 wherein theadjacent courses-of the first andsecond layer are butt joined, the joints of thesecond consisting of hardaluminum and polyimide; and b. a second layer formed from a film of amaterial selected from the class consisting of polyamide and polyimide.

